Electrical transfer switch and related method

ABSTRACT

The disclosure involves a transfer switch having a stationary frame and a front terminal matrix for connection to circuit boards undergoing test. There are two stationary connectors mounted on the switch frame. A platform is supported by the frame for reciprocating movement between first and second positions. Such platform has two movable connectors thereon and when the platform is in the first position, one of the movable connectors engages or “plug-connects” to one of the stationary connectors. When the platform is in the second position, the other movable connector plug-connects to the other stationary connector. The stationary connectors are electrically coupled to respective test devices, e.g., a load board and a signal bus. Thus, the boards under test can be connected to one or the other of the test devices by shifting the position of the platform. A new method is also disclosed.

RELATED APPLICATIONS

This application is a division of U.S. Ser. No. 09/221,501, and a filingdate of Dec. 28, 1998, now abandoned which is a division of U.S. Ser.No. 09/001,236, and a filing date of Dec. 30, 1997, now U.S. Pat. No.5,942,901, which is a division of U.S. Ser. No. 08/682,148, and a filingdate of Jul. 17, 1996, now U.S. Pat. No. 5,773,983.

FIELD OF THE INVENTION

This invention relates generally to apparatus for making and breakingelectrical circuits and, more particularly, to such an apparatus forsimultaneously making or breaking a relatively large number of suchcircuits.

BACKGROUND OF THE INVENTION

Depending upon the circuit board application, purchasers of electronicprinted circuit boards (PCBs) may require no more than routinereliability or, in sharp contrast, may require a very high degree ofreliability. A toy having a PCB would be in the former category whilemilitary aircraft, certain automotive applications and the like wouldclearly be in the latter.

One way to help assure a high level of reliability (or, conversely, tocull out PCBs which may exhibit “infant mortality” or premature failure)is to “stress screen” them. Such screening is by placing the PCBs in achamber, the interior air temperature of which is repetitively cycledbetween about 120° C. and about −60° C. over a relatively-short periodof time, i.e., well less than one hour or so.

In one exemplary test chamber arrangement, the chamber has a removablewall mounted on and forming a component of a wheeled cart. That side ofthe wall at the chamber interior has a fixture for mounting PCBs thereonduring test. On the opposite side of the wall, the cart has a rack onwhich instruments or the like are mounted. Feedthrough devices extendthrough separate respective openings in the removable wall and connectto PCBs in the fixture and to the instruments on the rack. Thisarrangement is used in a known test method including connecting the PCBsto instruments during stress screening—no switching is involved. In theparlance of the industry, this is known as Class A testing.

Another known PCB testing method includes switching the PCBs between aload board and a signal bus while such PCBs are undergoing thermalstress screening. Individual relays are used to switch each electricallead. Since each relay can handle but a single circuit, the number ofrelays required is, in general, equal to the number of wires or leadsextending from the PCBs under test. Thus, installations with more than100 relays are common. Relays can be troublesome, both from thestandpoint of undesirably-high contact resistance and with respect toreliability.

Heretofore, those conducting “switched” testing as well as non-switchedor Class A testing purchased (and stored and maintained) two carts, oneconfigured for PCB switching and the other configured for Class Atesting. A leading manufacturer of such carts and related equipment isRPI, Inc. of Racine, Wisconsin.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a transfer switch andrelated method overcoming some of the problems and shortcomings of theprior art.

Another object of the invention is to provide a transfer switch andrelated method which result in substantially improved reliability.

Another object of the invention is to provide a transfer switch whichexhibits decreased contact resistance.

Yet another object of the invention is to provide a transfer switchcapable of switching a large number of electrical circuitssimultaneously.

Another object of the invention is to provide a transfer switch andrelated method which are useful for both switched testing and Class Atesting.

Still another object of the invention is to provide a transfer switchand related method useful in cart-based stress testing to reduce thenumber of carts required to be used. How these and other objects areaccomplished will become more apparent from the following descriptionsand from the drawings.

SUMMARY OF THE INVENTION

Aspects of the invention involve a switch which transfers wiredconnections from printed circuit boards undergoing test to either afirst or a second device for testing the boards. This type of stressscreening is sometimes referred to as a “burn-in” test. In a specificembodiment, the devices may comprise a load board and a signal bus,respectively. The switch is capable of transferring a large number ofwired connections, e.g., 200 or so, simultaneously.

The switch has a frame with plate-like first and second spaced-apartmounting members. There are first and second stationary connectors whichare respectively supported by such mounting members. Parallel guideposts (four in the preferred embodiment) extend between the mountingmembers and function as bearing shafts for the moving platform describedbelow.

The switch also has an actuator-positioned platform supported by theframe for reciprocating movement between a first position and a secondposition. Such platform slides along the guide posts when the platformmoves with respect to the frame.

The platform has first and second movable connectors mounted on it. Suchconnectors are movable in the sense that they move with the platformrather than being movable with respect to the platform.

When the platform moves to the first position, the first connectorsengage with one another and when the platform moves to the secondposition, the second connectors engage with one another. Morespecifically, the first connectors engage with one another by“plug-connecting” the first movable connector on the platform to thefirst stationary connector on the first mounting member. In thealternative, the second movable connector is plug-connected to thesecond stationary connector. In turn, the first and second stationaryconnectors are electrically coupled by wiring harnesses or the like torespective test devices, i.e., to the exemplary load board and signalbus, respectively.

A linear actuator, e.g., a pneumatic or hydraulic cylinder or anelectrical solenoid, extends between the second mounting member and theplatform for moving the platform between the first and second positions.The actuator has a body fixed with respect to the second mounting memberand a reciprocating portion (a piston or solenoid armature, for example)extending between the body and the platform.

In another aspect of the invention, the switch platform has a pluralityof terminals supported thereon. In a preferred embodiment, the terminalsare on one or two boards configured somewhat like printed circuitboards. However, there are no printed circuits thereon and each terminalis slightly spaced from and electrically isolated from all otherterminals.

Each terminal is electrically coupled to the movable connectors on theplatform and to an input terminal matrix at what is referred to as thefront of the switch. Such matrix is connected (by means described below)to the printed circuit boards undergoing test.

In an exemplary application, the new transfer switch is used incombination with the load board and signal bus mentioned above and withan environmental test chamber containing circuit boards to be tested.Such chamber has a relatively-thick insulated wall with at least oneopening through it. The switch includes a feedthrough portion which isfixed with respect to the frame and which extends through the wallopening. Such feedthrough portion has an input terminal matrix fixedthereon and coupled to the circuit boards. The load board iselectrically coupled to the first stationary connector and the signalbus is electrically coupled to the second stationary connector.

The circuit boards are connected through the terminal matrix to theplatform terminals by “hard” wiring. The platform terminals areconnected to both the first and second movable connectors on theplatform. Similarly, the first and second stationary connectors areelectrically coupled to the first and second test devices, respectively.

When the switch platform is in the first position, the circuit boardsunder test are connected through the hard wiring to the terminals andthence to the first stationary connector via the first movable connectorand to the first test device. And when the switch-platform is shifted tothe second position, the circuit boards under test are connected via thehard wiring to the terminals and thence to the second stationaryconnector via the second movable connector and to the second testdevice. Stated another way, the printed circuit boards can be connectedto either test device by reciprocating the actuator and the platform. Inan actual test, the platform may be reciprocated hundreds or eventhousands of times to test a particular batch of printed circuit boardsin the test chamber.

Another aspect of the invention involves the combination of (a) a cart,(b) a plurality of transfer switches mounted on the cart, and (c) anenvironmental test chamber containing circuit boards to be tested. Eachtransfer switch includes a frame, a reciprocating platform andstationary and movable connectors as described above.

The test chamber includes a wall having a plurality of sockets mountedthereon. The cart and its transfer switches are spaced from the chamberand there is a separate cable harness extending between each socket anda respective transfer switch. In one specific embodiment, the cableharness connects to a terminal matrix on the transfer switch. In anotherspecific embodiment (configured to reduce contact resistance to aminimum), the cable harness is “hard-wired” and connects directly to theterminals on the platform without using an intervening terminal matrix.

Another aspect of the invention involves a new method for testingprinted circuit boards. Such method includes the steps of providing atransfer switch electrically connected to the circuit boards and havinga platform mounted for reciprocating movement between a first positionand a second position. Also provided are first and second test deviceswhich are fixed with respect to the platform. The platform is moved tothe first position, thereby connecting the circuit boards to the firsttest device and then such platform is moved the second position, therebyconnecting the circuit boards to the second test device.

In a more specific aspect of the method, the platform includes aplurality of terminals supported thereon. The switch includes an inputterminal matrix fixed with respect to the platform. Wires extend betweenthe matrix and the terminals and the first moving step includes flexingthe wires in a first direction. The second moving step includes flexingthe wires in a second direction.

Minimized wire flexure is an advantage of the new switch and the newmethod related thereto. The wires include a first wire extending along afirst wire axis when the platform is in the first position and extendingalong a second wire axis when the platform is in the second position.Both wire axes are slightly angular with respect to the switch longaxis. The included angle between the wire axes is less than about 10°.And depending upon the length of the switch and the particular wirebeing considered, the including angle between the wire axes may be evenless than 5° or so.

In yet another aspect of the new method, the first moving step includesrepositioning the movable platform connectors along an axis coincidentwith the stationary connectors. And most preferably, the platform isreciprocated in two directions which are 180° apart.

Other aspects of the invention are set forth in the following detaileddescription and in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view of one type of an exemplary cart-basedcircuit board test system with which the new transfer switch may beused.

FIG. 2 is a side elevation view of the transfer switch.

FIG. 3 is a representative side elevation view showing aspects of thetransfer switch of FIG. 2.

FIG. 4 is a top plan view of the switch of FIG. 2 taken along theviewing plane 4—4 thereof.

FIG. 5 is a front elevation view of the switch of FIG. 2 taken along theviewing axis VA5 thereof.

FIG. 6 is a rear elevation view of the switch of FIG. 2 taken along theviewing axis VA6 thereof.

FIG. 7 is a cross-sectional elevation view of the switch of FIG. 2 takenalong the viewing plane 7—7 thereof.

FIG. 8 is a cross-sectional elevation view of the switch of FIG. 2 takenalong the viewing plane 8—8 thereof.

FIG. 9 is an enlarged view of a terminal lug, one of a large number ofsuch lugs used on the switch of FIG. 2.

FIG. 10 is a representative side elevation view generally like that ofFIG. 3 and showing other aspects of the transfer switch of FIG. 2.

FIG. 11 is a perspective view of another type of exemplary cart-basedcircuit board test system with which the new transfer switch may beused.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Before describing the new transfer switch 10 in detail, it will behelpful to have an understanding of one of the ways in which such switch10 may be used. Referring first to FIGS. 1, 2 and 3, FIG. 1 shows acart-based system 11 for stress-screening printed circuit boards 13.Such system 11 includes a wheel-mounted cart 15 and a companion testchamber 17 having insulated walls 19 and an open side 21. The cart 15has an upright wall 23 and the open side 21 and the wall 23 arecooperatively configured so that such wall 23 fits snugly into the openside 21 during testing.

Mounted on the inward side of the wall 23 is a fixture 25 for supportinga number of printed circuit boards 13. The wall 23 has several openings29 through it, each of which has a feedthrough portion 31 of a transferswitch 10 extending therethrough. In a system 11 used to transfer theprinted circuit boards 13 between first and second test devices 33, 35,e.g., a load board 33 a and a signal bus 35 a, respectively, the system11 also includes such devices 33, 35. The new switch 10 is capabile oftransferring a large number of wired connections simultaneously. In aspecific embodiment, two hundred or so connections may be switched.

Referring also to FIGS. 4, 5, 6, 7 and 8, the new switch 10 will now bedescribed. The switch 10 has a frame 39 with substantially planar,plate-like first and second spaced-apart mounting members 41, 43,respectively. Four parallel guide posts 45 extend between the mountingmembers 41, 43, are arranged in a four-corner pattern defining thecorners of a rectangle and function as bearing shafts for the movingplatform described below.

First and second stationary connectors 49 and 51, respectively, aremounted on and supported by the mounting members 41 and 43,respectively. In a highly preferred embodiment, such connectors 49, 51are 102-pin modular male connectors available from Hypertronics Co. Andwhile the switch 10 functions quite satisfactorily with the connectors49, 51 to switch up to about 100 circuits simultaneously, a highlypreferred embodiment of the switch 10 includes third and fourthstationary connectors 53 and 55, respectively. Such connectors 53, 55are of the type described above.

Forward of the mounting members 41, 43 is a feedthrough portion 31having a front plate 57 and a holding plate 59 with rod-like supports 61extending therebetween. A specific embodiment includes four inwardsupports 61 a arranged in a four-corner pattern and foursimilarly-arranged outward supports 61 b. Mounted at the front of theswitch 10 is a terminal matrix 63 comprising a 120-contact femaleconnector 65 and a 90-contact female connector 67, both available fromElco.

Mounted at the rear of the switch 10, rearward of the end plate 71spanning the mounting members 41, 43, is a pair of vertically-spaced104-pin receptacle housings 73, 75 as made by Amp, Inc. Such housings73, 75 may be used to connect a test device 35, e.g., a signal bus 35 a,to the switch 10 and to the boards 13 undergoing test.

Adjacent to the housings 73, 75 is a pair of spaced, parallel 100-pinedge card connectors 77, 79 as made by Sullins. Such edge cardconnectors 77, 79 may be used to connect another test device 33, e.g.,load boards 33 a, to the switch 10 and to the boards 13 undergoing test.

Details of the switch platform 47 will now be set forth. Referringparticularly to FIGS. 2 and 7, an actuator-positioned platform 47 issupported by the frame 39 for reciprocating movement between a first orupward position 83 shown in solid outline and a second or downwardposition represented by the dashed line 85. Such platform 47 slidesalong the guide posts 45 when the platform 47 moves with respect to theframe 39.

As shown FIG. 7, the platform 47 has first and second mounting plates87, 89, respectively, which are parallel to one another and spacedapart. Bearing blocks 91 are fastened to and extend between such plates87, 89 for providing platform rigidity.

The platform 47 also includes a pair of terminal boards 93 and 95extending between vertically-spaced edges of respective mounting plates87, 89. Each such terminal board 93, 95 has an insulating substrate 97and a plurality of three-point lugs 99 thereon as shown in FIG. 9. Eachlug 99 is made of electrically-conductive material, is supported by thesubstrate 97 and is electrically isolated from other lugs 99. Thepurpose of such lugs 99 is described below.

Referring again to FIGS. 2 and 7, the platform 47 has first and secondmovable connectors 101, 103, respectively, mounted on the first andsecond mounting plates 87, 89, respectively. In a highly preferredembodiment, such connectors 101, 103 are 102-pin modular femaleconnectors available from Hypertronics Co. And while the switch 10functions well with the connectors 101, 103 to switch up to about 100circuits simultaneously, a highly preferred embodiment of the switch 10includes third and fourth movable connectors 105 and 107, respectively.Such connectors 105, 107 are of the 102-pin type described immediatelyabove.

Referring now to FIGS. 2, 7 and 8, a linear actuator 109, e.g., apneumatic or hydraulic cylinder 109 a or an electrical solenoid, extendsbetween the first mounting member 41 and the platform 47 for moving theplatform 47 between the first and second positions 83, 85. The actuator109 has a body ill attached to the first mounting member 41 and areciprocating portion 113 (a piston or solenoid armature, for example)extending between the body 111 and the platform 47. When thereciprocating portion 113 is retracted, the platform 47 is in its firstor upward position 83 and when such portion 113 is extended, theplatform 47 is in its second or downward position 85.

When the platform 47 moves to the first position 83, the first and thirdmovable connectors 101, 105 plug-connect to the first and thirdstationary connectors 49, 53, respectively. And when the platform 47moves to the second position 85, the second and fourth movableconnectors 103, 107 plug-connect to the second and fourth stationaryconnectors 51, 55 respectively.

FIGS. 3 and 7 and the following description explain how the switch 10 isused to connect a printed circuit board 13 under test with either of twotest devices 33, 35, e.g., the exemplary load board 33 a or signal bus35 a. While the connection arrangement is shown for only a singleelectrical point 115 on the printed circuit board 13, it is to beappreciated that there may be on the order of 200 such points 115, eachconnectable to the load board 33 a or to the signal bus 35 a byenergizing the actuator 109 and moving the platform 47.

In one embodiment, the electrical point 115 is coupled to the terminalmatrix 63 from which a wire 119 extends to a lug 99. A wire 121 alsoextends between the lug 99 and the first movable connector 101 andanother wire 123 extends between such lug 99 and the second movableconnector 103. The positions of the connectors 101, 103 and lug 99 shownin solid outline are those when the platform 47 is in its first position83. And the positions of the connectors 101, 103 and lug 99 shown indashed outline are those when the platform 47 is in its second position85. Of course, the first and second stationary connectors 49, 51 do notmove with platform movement.

In another embodiment shown in FIG. 10, the switch 10 is free of aterminal matrix 63 and each electrical point 115 is coupled directly toa separate lug 99 by a separate wire 119 a, 119 b. Wires 121 a, 121 b,123 a, 123 b also extend between each lug 99 and the first and secondmovable connectors 101, 103. In this embodiment, the contact resistanceotherwise imposed on the circuit by the terminal matrix 63 (which in anyevent is quite low) is nevertheless avoided.

Referring next to FIGS. 2, 3 and 11 another aspect of the inventioninvolves the combination of (a) a cart 15, (b) a plurality of transferswitches 10 mounted on the cart 15, and (c) an environmental testchamber 17 a containing circuit boards 13 to be tested. Such circuitboards 13 are loaded from the side 125 of the chamber 17 a.

Preferably opposite the side 125, the test chamber 17 a includes a wall127 having a plurality of sockets 129 mounted thereon. The cart 15 andits transfer switches 10 are spaced from the chamber 17 a and there is aseparate cable harness 131 extending between each socket 129 and arespective transfer switch 10. In one specific embodiment, each cableharness 131 connects to a separate terminal matrix 63 on a respectivetransfer switch 10. In another specific embodiment apparent from FIG. 10and the related description, (configured to reduce contact resistance toa minimum), each cable harness 131 is “hard-wired” and connects directlyto the lugs 99 on the platform 47 of a separate switch 10 without usingan intervening terminal matrix 63. (Depending upon the specific testarrangement, the number of switches 10 on the cart 15 or actually in usemay or, as shown in FIG. 11, may not be equal to the number of sockets.)

Another aspect of the invention involves a new method for testingprinted circuit boards 13. Such method includes the steps of providing atransfer switch 10 electrically connected to the circuit boards 13 andhaving a platform 47 mounted for reciprocating movement between a firstposition 83 and a second position 85. Also provided are first and secondtest devices 33, 35 which are fixed with respect to the platform 47. Theplatform 47 is moved to the first position 83, thereby connecting thecircuit boards 13 to the first test device 33 and then such platform 47is moved the second position 85, thereby connecting the circuit boards13 to the second test device 35.

In a more specific aspect of the method, the platform 47 includes aplurality of lugs 99 supported thereon. The switch 10 includes an inputterminal matrix 63 fixed with respect to the platform 47. Wires 119extend between the matrix 63 and the lugs 99 and, noting FIGS. 3 and 10,the first moving step includes flexing the wires 119 in a firstdirection, e.g., upwardly. The second moving step includes flexing thewires 119 in a second direction, e.g., downwardly.

Minimized wire flexure is an advantage of the new switch 10 and the newmethod related thereto. The wires 119 include a first wire (wire 119 andFIG. 3) extending along a first wire axis 135 when the platform 47 is inthe first position 83 and extending along a second wire axis 137 whenthe platform 47 is in the second position 85. Both wire axes 135, 137are slightly angular with respect to the switch long axis 139. Theincluded angle A1 between the wire axes 135, 137 is less than about 10°.And depending upon the length of the switch 10 and the particular wire119 being considered, the including angle A1 between the wire axes 135,137 may be even less than 5° or so.

In yet another aspect of the new method, the first moving step includesrepositioning the movable platform connectors 101, 103 along an axis 141coincident with the stationary connectors 49 and 51 and with the movableconnectors 101 and 103. And most preferably, the platform 47 isreciprocated in two directions, e.g., n directly upward and directlydownward, which are 180° apart.

As used herein, such terms as “upward” and “downward” are forconvenience in explanation. It should be understood that the new switch10 is capable of operating in any position.

While the principles of the invention have been shown and described inconnection with a few preferred embodiments, it is to be understoodclearly that such embodiments are by way of example and are notlimiting.

What is claimed:
 1. An environmental test system for use in testing aprinted circuit board, comprising: a testing chamber for receiving theprinted circuit board therein; and a transfer switch for selectivelyconnecting the circuit board between first and second test devices, thetransfer switch extending along a switch axis and including: a frameincluding first and second mounting members which are spaced apart fromeach other; a first stationary connector supported on said firstmounting member of said frame and operatively connected to the firsttest device; a second stationary connector supported by said secondmounting member of said frame and operatively connected to the secondtest device; a platform supported on said frame between said first andsecond mounting members for linear reciprocating movement therebetween,said platform including first and second movable connectors thereonwhich are operatively connected to the printed circuit board; anon-manual actuator coupled to said platform for linearly moving theplatform along a longitudinal axis between the first and second mountingmembers, said longitudinal axis, wherein said actuator moves saidplatform between a first position connecting said first movableconnector to said first stationary connector and a second positionwherein said first movable connector is separated from said firststationary connector and wherein said movable connector is connected tosaid second stationary connector; and at least one guide post extendingbetween said first and second mounting members, wherein said platformmoves linearly along said guide post under urging from said actuator. 2.The environmental test system of claim 1 wherein said actuator is a soleactuator moving said platform.
 3. The environmental test system of claim2 further comprising a terminal matrix and an end plate and saidplatform is between said terminal matrix and said end plate.
 4. Theenvironmental test system of claim 1 wherein said testing chamberincludes plural sockets mounted thereon such that said transfer switchand at least one of said sockets are connected to one another by a cableharness.
 5. The environmental test system of claim 1, further comprisinga feedthrough port connected to each of said first and second mountingmembers.
 6. An environmental test system for testing printed circuitboards, comprising: a test chamber for receiving the printed circuitboards therein; and a transfer switch extending along a switchlongitudinal axis and including: a frame including first and secondmounting members which are spaced apart from each other, first and thirdstationary connectors supported on said first mounting member; secondand fourth stationary connectors supported by said second mountingmember; a platform for linearly reciprocating movement and having first,second, third and fourth movable connectors thereon which areoperatively connectable to the printed circuit boards; a non-manualactuator coupled to said platform for linearly moving the platform alonga longitudinal axis, said actuator moving said platform between a firstposition connecting said first movable connector to said firststationary connector and said third movable connector to said stationaryconnector and a second position connecting said second movable connectorto said second stationary connector and said fourth movable connector tosaid fourth stationary connector; and at least one guide post extendingbetween said first and second mounting members, wherein said platformmoves linearly along said guide post under urging from said actuator. 7.The environmental testing system of claim 6 wherein said first andsecond stationary connectors are coincident with a connector axis, andsaid connector axis is parallel to said actuator axis.
 8. Theenvironmental testing system of claim 6 wherein said testing chamberincludes plural sockets mounted thereon such that said transfer switchand at least one of said sockets are connected to one another by a cableharness.